Many types of motion production devices have been developed for imparting motion to a load, such as in connection with vehicle simulation equipment. Traditional vehicle simulation motion production equipment is designed to impart motion to an occupant or to occupants of a vehicle simulator in such a manner as to cause physiological sensations similar to, if not identical to, those that would be felt by an operator of a real vehicle under certain circumstances. Typically, vehicle simulation equipment is designed to emulate automobile or aircraft operation.
One of the primary and long felt problems encountered in the design of vehicle simulators has been reversal of motion. Specifically, when there is motion in one axis, the task of smoothly stopping that motion and reversing the motion along the same axis has proven to be difficult to accomplish.
Indeed, to cause the physiological sensations associated with operating a real vehicle, it is important to be able to reverse direction along any axis of motion smoothly. This is because the operators of real vehicles generally experience relatively smooth reversals and other changes in direction. For example, as a driver of a real automobile drives along a highway, the automobile will tend to smoothly oscillate up and down. Additionally, real automobiles tend to smoothly impart acceleration forces to the driver as the vehicle, from time to time, slows down or speeds up. During these periods of acceleration, the driver, as well as any other vehicle occupant, will physiologically sense certain smooth changes in direction. These smooth reversals and changes in direction and the associated acceleration forces are what traditional vehicle simulation motion production equipment strives to but has been unable to effectively, efficiently, and inexpensively emulate.
Prior attempts to create smooth reversals of direction and smooth accelerations have been largely unsuccessful. For example, many relatively low-cost, arcade-type, motion simulators are driven by an electric motor coupled to a series of gears. When this type of simulator attempts to reverse or otherwise change the simulator's direction of motion, it does so abruptly, thus imparting to the operator, or other simulator occupant, an artificial feeling unlike the smooth physiological sensations associated with operating a real vehicle. One of the primary limitations of this type of simulator is that it is gear-driven. Using gears to cause reversals and other changes of the direction of motion has certain problems associated with it, such as: the reversal of motion has a slower response time, the reversal of motion is highly abrupt, and the reversal of motion is often accompanied with clanking because of gear lash. All of these problems contribute in creating an unrealistic simulation of an actual driving experience and collectively hamper the vehicle motion simulation.
Other attempts to create realistic motion simulation devices also have certain limitations associated with them. For example, a relatively high cost motion simulation device used primarily for flight simulation has also been developed. This device is referred to in the trade as a "hexapod" system. The hexapod system employs a high capacity pump in fluid communication with six valves with each valve being coupled to a piston/cylinder assembly. By selectively opening and closing the variable orifice valves, the piston/cylinder assemblies are driven to change the position of the load.
The hexapod piston/cylinder assemblies are unique in that they employ a piston that is designed to leak fluid. The piston/cylinder assemblies required for this type of motion simulator typically cost five to ten times as much as conventional piston/cylinder assemblies. As such, these piston/cylinder assemblies are, unfortunately, prohibitively expensive for use in many applications.
It has also been proposed to use electromagnets to impart motion in motion simulation devices. The use of electromagnets, too, is problematic because electromagnets have been found to be prohibitively expensive to produce, and operate for many applications. An additional limitation associated with the use of electromagnets to impart motion in motion simulation devices is that it has been found that electromagnets are generally unable to efficiently and accurately produce the range of forces required to satisfactorily drive motion simulation equipment.
The use of conventional four-way valves has also proven to be unsatisfactory in motion simulation devices. Specifically, four-way valves cost on the order of two to four times as much as conventional proportional valves. As such, four-way valves are prohibitively expensive for many applications, particularly in applications, such as in vehicle simulators where several valves are required. In addition to being more expensive, it has been found that four-way valves do not perform uniformly over a wide range of loads because of their fixed physical construction. As such, a 90 pound person and a 300 pound person operating the same vehicle simulator will get very different rides due to the difference in the magnitude of the loads imposed.